Lok Sabha speaker Somnath Chatterjee has decided to resign from his post as the Left parties have withdrawn support to the UPA government, which is set to face the trust vote on July 22.

Sources said that Chatterjee will submit his resignation soon.

The vote of confidence has been necessitated in the wake of the Left pulling out of the government on the issue of the Indo-US nuclear deal.

However, CPI(M) General Secretary Prakash Karat has denied the reports, saying no decision has been taken to ask Chatterjee to quit the post.

On Wednesday, Karat had said that Chatterjee would decide on his own whether to resign as Speaker of the House.